test(keeper): assert one contract's failure cannot stop a tick

[0dillon]

Summary

runTick wraps each maintainContract call in a try/catch so that one contract's failure is
logged and the loop continues. This is the property that keeps a keeper maintaining twenty contracts
when the first one is broken, and nothing tests it.

It is also the property most likely to be destroyed by a well-meaning refactor. Moving the try/catch
outward, or letting an await escape it, turns one bad contract into a daemon that stops working
and gives no clear sign why.

Acceptance Criteria

• A test runs a tick over several contracts where a middle one throws, and asserts every other
  contract was still maintained.
• The failure is asserted to have been logged with the failing contract's ID.
• A test covers the first contract failing and the last contract failing, since off-by-one
  handling differs at the ends.
• The existing abort behaviour is not broken: a tick aborted mid-loop still stops immediately
  and logs contractsMaintained and contractsRemaining.
• Verified by mutation: remove the try/catch, confirm the test fails.

Tech Stack

TypeScript 5.7 on Node 22+ (CI runs 22 and 24), ESM with moduleResolution: "NodeNext" — relative
imports need the .js extension. @stellar/stellar-sdk is pinned to an exact version; verify RPC
API shape against the installed copy, not against documentation. Tests are Vitest under test/ and
run without a network. npm run format:check, npm run lint, npm run build and npm test must
all be clean.